Silicone rubber fouling-resistant compositions are described for example in GB-A-1307001, 1470465, 1581727 and 2141436, EP-B-16195 and 32597, EP-A-89071 and 329375 and U.S. Pat. No. 3,702,778 and U.S. Pat. No. 4,525,565. They have significant advantages over conventional antifouling compositions containing marine biocides which are gradually leached from the paint. The silicone rubber coatings rely on their low surface energy, rather than on biocides, to inhibit settlement of marine organisms. Conventional anti-fouling paints eventually become ineffective as all their biocide is released. Silicone rubber coatings are potentially capable of retaining their low energy surface indefinitely.
The silicone rubber fouling-resistant coatings are generally based on a hydroxy-functional polydiorganosiloxane, usually an alpha, omega-dihydroxypolydiorganosiloxane, or a material which is hydrolysable to such a hydroxy-functional polydiorganosiloxane. These hydroxy-functional polydiorganosiloxanes, sometimes known as silicone gums, are curable through their hydroxy groups, and fouling-resistant coating compositions based on them include a crosslinking agent reactive with SiOH groups or hydrolysable to a substance reactive with SiOH groups. EP-B-32597 and EP-A-329375 describe two-pack compositions in which a crosslinking agent such as ethyl silicate is packaged separately from the hydroxy-functional polydiorganosiloxane. Single-pack compositions in which the crosslinking agent contains hydrolysable groups such as acyloxy or ketiminoxy groups are described for example in U.S. Pat. No. 4,525,565 and EP-B-32597.
Such single-pack compositions have the disadvantage that substantial excess of the crosslinking agent needs to be used to obtain a storage-stable composition as taught by U.S. Pat. No. 4,973,623. If the molar ratio of crosslinking agent to the silicon-bonded hydroxyl groups of the hydroxy-functional polydiorganosiloxane is low, the composition is liable to gelation on storage.